In order to produce hydrocarbons, such as oil and gas from a subterranean reservoir, either onshore or offshore, a borehole is drilled through various layers of rock in a formation. A casing may be cemented into the formation along all or part of the borehole to create a wellbore, and a production string is inserted into the wellbore to convey the hydrocarbons to the surface. In other instances, in place of cement, annular packers may be used to seal the casing to the wellbore to prevent the longitudinal flow of fluids along the exterior of the casing. The casing in many instances becomes the production tubular for the wellbore such that the annular packers or the cement isolates each formation zone or portion of a formation zone from one another.
With the casing cemented into the well or the annular packers deployed along the length of the casing, the casing is effectively sealed against allowing any fluids to flow from the formations to the interior of the casing. With the casing effectively sealed against fluid flow, positive fluid downward through the casing is limited at best without access to the exterior of the casing making it difficult if not impossible to pump a ball or a dart through the casing to actuate the toe sleeve.
Therefore access to the exterior of the casing and therethrough to the various formation zones is needed. One means of accessing the exterior of the casing is to utilize a plug and perforate operation where a plug, a setting tool, and a perforating gun sleeve are run into the well on wireline or coil tubing using gravity or a tractor to pull the tool into position. If a sleeve system is used then actuation is limited to mechanical manipulation from the surface such as by the use of coil tubing, slick line, or electric line.
It has been found that it is possible to establish sufficient fluid flow through the casing and into the adjacent formation thereby allowing the subsequent activation of sliding sleeves by dropping balls, plugs, or darts by use of pressure to establish fluid flow with the exterior the casing where the pressure required to establish fluid flow to the exterior is preset at the surface to correspond to the requirements of the well.
Once the casing is in place in the wellbore and either cemented or all of the packers actuated fluid access to the exterior is required to facilitate the subsequent activation of sliding sleeves or other tools by dropping balls, plugs, or darts. In order to provide such fluid access to the exterior of the casing a toe sleeve subassembly is installed at the bottom of the casing. The toe sleeve subassembly has at least one port through which fluid may flow thereby establishing fluid flow through the casing and allowing the activation of ball actuated tools.
The port is provided with a burst disk where the burst disk has to be of sufficient strength to maintain a predetermined pressure during other operations that may be conducted prior to the establishment of fluid flow to the exterior of the casing. In order to operate the burst disk and establish circulation in the wellbore the casing has to be pressurized to some predetermined amount in excess of the pressure required during other operations conducted prior to the establishment of fluid flow to the exterior of the casing. Once the burst disk has burst fluid may then be pumped down through the interior of the casing and into the adjacent formation allowing balls darts or plugs to be pumped down through the casing to actuate other sleeves or tools in the casing above the toe sleeve.
In many instances over the course of the life of a well it may become necessary to prevent access through many or all of the access points, such as sliding sleeves, to the exterior of the well. In instances where access is provided by sliding sleeves a tool, such as a fishing tool, may be run into the well to close each of the sliding sleeves. However since the toe subassembly is operated by means of a burst disk a bridge plug is required to be run in and an operation separate from the operation to close each of the sliding sleeves. There is a need to easily close the toe subassembly without running in a separate bridge plug.